Electronic loads are usually comprised of banks of MOSFET's tied in parallel and are operated in the active region. They dump power into the active devices and are used in testing power supplies. One way to drive down the cost is to parallel resistive loads with conventional MOSFET loads to enable the resistors to share power loss. Resistors are cheaper than MOSFET's and can be operated at higher temperatures. For example, it is known from U.S. Pat. No. 8,242,629 to Palatini, et al. to add passive resistors in parallel to the MOSFETS. However, it is believed that the response would be slow when switching the resistors, and power cannot be distributed equally among the resistors.
What is needed is a switching matrix of resistors that would share losses between resistors and the resistors would be in series with the active load to enable a quick response and low ripple when switching. Putting resistors in series with the collector of bipolar devices or in series with the drain of MOSFET devices is a common method for removing heat from the power device.